Pathogens and Disease

Pathogens and disease for schools and colleges

Pathogens are microorganisms capable of causing disease. There are hundreds of different bacteria capable of causing disease. Different genes and characteristics of bacteria are what determine the diseases they cause.

Bacteria capable of causing disease are known as pathogens. Many pathogens are 'opportunistic', meaning they live most of their lives within the body not causing any damage. This is known as commensalism. When the human body becomes immuno-compromised (following chemotherapy for example) these opportunistic pathogens may strike.

 Humans are targets for a variety of pathogens, which cause many different diseases. The diseases caused by a particular pathogen depend of the characteristics of the pathogen, but also the area of the body in which it grows.

Common pathogens

Multiple species of bacteria can in some cases, all cause the same disease. For example, pneumonia is a common inflammatory disease of the lung, effecting the alveoli. Symptoms of pneumonia include: coughing, chest pain and fever. The disease can be cause by: Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, Neisseria meningitis and many more.

On the other hand, many of these bacteria can cause several different diseases. N. meningitidis for example, in addition to pneumonia, can cause meningitis and septicaemia (blood poisoning).

 Read more about some important human pathogens through the links below.


Above- two falsely coloured electron microscopy images of Klebsiella pneumoniae (left) and Legionella pneumophila. Both bacteria are common human pathogens and are involved in the development of pneumonia.



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